1. Field of the Invention
The present invention relates to an electrically-driven closed scroll compressor for use in, for example, an air conditioner, a refrigerator or the like.
2. Description of Related Art
Japanese Laid-open Patent Publication (unexamined) No. 3-149382 discloses a generally available electrically-driven closed scroll compressor as shown in FIGS. 14 to 17.
Referring to FIG. 14, a compression mechanism 102, an electric motor (not shown), and a crank shaft 103 for transmitting a rotational force of the electric motor to the compression mechanism 102 are accommodated within a closed vessel 101. The closed vessel 101 is provided with a suction pipe 104 rigidly secured thereto for introducing a low-pressure refrigerant thereinto and with a discharge pipe (not shown) rigidly secured thereto for discharging a high-pressure refrigerant compressed by the compressor mechanism 102 to the outside of the closed vessel 101.
The scroll compressor shown in FIG. 14 operates as follows.
The rotational force generated by the operation of the electric motor is transmitted to the compression mechanism 102 via the crank shaft 103 and causes an eccentric bearing 105 to undergo an eccentric rotational motion. The eccentric bearing 105 rotatably supports an orbiting shaft 107 of an orbiting scroll 106. An Oldham ring 108 is provided to prevent the orbiting scroll 106 from rotating about its own axis while permitting it to undergo an orbiting motion relative to a stationary scroll 109 with the orbiting and stationary scrolls 106 and 109 being in engagement with each other.
As a result, the low-pressure refrigerant introduced into the closed vessel 101 through the suction pipe 104 passes through a suction port 110 defined in the compression mechanism 102 and is trapped into two volume-variable and radially symmetric working pockets 111 defined between an orbiting scroll wrap 117 of the orbiting scroll 106 and a stationary scroll wrap 118 of the stationary scroll 109. Then, the refrigerant trapped into each working pocket 111 experiences a decrease in volume and an increase in pressure as it approaches a center discharge port 112 and is subsequently discharged into a high-pressure chamber 119 through the center discharge port 112 and then to the outside of the closed vessel 101 through the discharge pipe.
FIGS. 15A to 15D depict a compression process during which the refrigerant trapped in the working pockets 111 is compressed by the compression mechanism 102. FIG. 15A indicates the state at an orbiting angle of 0.degree. at which the introduction of the low-pressure refrigerant into the two working pockets 111, particularly identified by A and B, is completed. FIGS. 15B and 15C indicate the states at orbiting angles of 90.degree. and 180.degree., respectively, and also indicate a progressive reduction in volume of the working pockets 111 (A and B). FIG. 15D indicates the state at an orbiting angle of 270.degree. at which the two working pockets 111 communicate with the center discharge port 112 so that the high-pressure refrigerant may be discharged from the center discharge port 112.
The pressure of the refrigerant inside the working pockets 111 acts to apply an axial or thrust force FI to the orbiting scroll 106 to move or float it away from the stationary scroll 109, and the magnitude of the thrust force FI varies continuously during the orbiting motion of the orbiting scroll 106. This thrust force FI is hereinafter referred to as a floating force. On the other hand, an orbiting end plate 113 of the orbiting scroll 106 confronts a flat portion 115 of a generally ring-shaped bearing member 114 secured to the stationary scroll 109 and is held in contact with a ring-shaped sealing member 116, which is received in a recess defined in the bearing member 114 on the flat portion 115 thereof and is coaxially aligned with the bearing member 114. That region on the orbiting end plate 113 which is defined internally of the sealing member 116 receives the pressure of the high-pressure refrigerant, while that region on the orbiting end plate 113 which is defined externally of the sealing member 116 receives an intermediate pressure between the pressure of the low-pressure refrigerant and that of the high-pressure refrigerant. The intermediate pressure can be obtained by communicating a space defined on one side of the bearing member 114, in which space the pressure of the high-pressure refrigerant acts, with another space defined on the other side of the bearing member 114, in which space the pressure of the low-pressure refrigerant acts, through a through-hole of a small diameter defined in the bearing member 114. Accordingly, it is possible to determine the magnitude of an axial or thrust force FO, which the refrigerant applies to the orbiting scroll 106 from the side of the sealing member 116 so as to press the orbiting scroll 106 against the stationary scroll 109, to a predetermined one by appropriately selecting the diameter of the sealing member 116, i.e. the area of the inner region. This thrust force FO is hereinafter referred to as a pressing force. The magnitude of the pressing force FO depends on only the pressure of the high-pressure refrigerant and the intermediate pressure between the pressure of the low-pressure refrigerant and that of the high-pressure refrigerant and is made constant during the orbiting motion of the orbiting scroll 106.
FIG. 16 schematically depicts a relationship between the floating force FI and the pressing force FO as viewed from the working pockets 111 towards the orbiting scroll wrap 117.
As shown in FIG. 16, a central point Fo of application of the pressing force FO moves so as to draw a circular orbit Do around a point P as the orbiting scroll 106 undergoes an orbiting motion. Because the sealing member 116 is coaxially aligned with the bearing member 114, the radius of the circular orbit Do is equal to an orbiting radius of the orbiting scroll 106, while the central point P of the circular orbit Do coincides with a central point O of the orbiting end plate 113 of the orbiting scroll 106. On the other hand, a central point Fi of application of the floating force FI moves so as to draw a circular orbit Di around a central point Q of development of a scroll curve forming the orbiting scroll wrap 117. Because the two working pockets 111 are radially symmetric, the radius of the circular orbit Di is equal to half the orbiting radius of the orbiting scroll 106. The pressing force FO is directed 180.degree. opposite to the floating force FI, and the central point Fo of application of the former is spaced a distance L from that Fi of the latter. This distance L varies with the orbiting motion of the orbiting scroll 106.
Because the orbiting and stationary scroll wraps 117 and 118 defining the working pockets 111 therebetween are formed so as to represent respective involute curves of a circle, the central point Q of development of the scroll curve referred to above is a central point of a basic circle of the involute curve which the orbiting scroll wrap 117 represents.
Also, because the central point Fo of application of the pressing force FO is spaced a distance L from that Fi of the floating force FI, the orbiting scroll 106 receives an overturning moment M in proportion to a value obtained by multiplying the floating force FI by the distance L.
FIG. 17 depicts a relationship among the pressing force FO, floating force FI, distance L, and overturning moment M with the axis of abscissa indicating an orbiting angle of the orbiting scroll 106. An orbiting angle of 0.degree. is an angle at which the introduction of the low-pressure refrigerant into the working pockets 111 is completed, and corresponds to the state of FIG. 15A. An orbiting angle of .alpha..degree. indicating a maximum floating force FI is an angle at which the working pockets 111 communicate with the center discharge port 112 defined in the orbiting scroll 106, and coincides substantially with an orbiting angle at which the distance L between the central point Fi of application of the floating force FI and the central point Fo of application of the pressing force FO is maximum. The floating force FI is minimum at an orbiting angle of .beta..degree..
Because the overturning moment M acting on the orbiting scroll 106 is proportional to the value obtained by multiplying the floating force FI by the distance L, the overturning moment M becomes very large at the orbiting angle of .alpha..degree. and takes a maximum value Mmax.
If a very large overturning moment M acts on the orbiting scroll 106, contact of the orbiting scroll 106 with the stationary scroll 109 cannot be maintained normal. As a result, the orbiting scroll 106 undergoes an orbiting motion in its inclined state, and leakage of the compressed refrigerant takes place between neighboring working pockets 111, resulting in a reduction in volume efficiency.
Also, biased contact takes place between the orbiting shaft 107 of the orbiting scroll 106 and the eccentric bearing 105 or between an outer peripheral portion of the orbiting end plate 113 of the orbiting scroll 106 and the stationary scroll 109, thus increasing wear and reducing the duration of life of the compressor itself. The biased contact also causes abnormal noise or vibration.
Furthermore, if a sealing member 116 having a relatively large diameter is mounted on the bearing member 114 to enlarge the pressing force FO and restrain a large overturning moment M from acting on the orbiting scroll 106 so that contact between the orbiting and stationary scrolls 106 and 109 may be always maintained normal during the orbiting motion of the orbiting scroll 106, a large sliding loss is generated on a contact area between the orbiting end plate 113 of the orbiting scroll 106 and the stationary scroll 109, resulting in a reduction in mechanical efficiency.